Method for manufacturing raised electrical contact pattern of controlled geometry

ABSTRACT

Spring contact elements are attached to terminals of an electronic component, which may be a semiconductor die. The spring contact elements may comprise a flexible precursor element. The precursor element may be over coated with a resilient material. The spring contact elements may be elongate and attached to the terminals at one end. The other end of the spring contacts may be spaced away from the electronic component.

BACKGROUND OF THE INVENTION

[0001] This invention relates in general to electronic assemblies andtesting thereof. In particular, the invention relates to a method ofmanufacture of protruding, controlled aspect ratio and shape contactsfor uses in interconnections of assemblies and testing thereof.

[0002] Interconnections which involve protruding electrical contacts areused extensively in packaging of electronics. Pin grid array packages,both plastic and ceramic, housing a variety of semiconductors, use areaarrays of pins as interconnect contacts for connection to circuitboards. Pins can be attached to their receiving package conductors byuse of a variety of methods. For ceramic packages, pins are insertedinto non-reacting brazing fixtures and are then gang-brazed tocorresponding conductive terminals on the package. This approach ischaracterized by significant non-recurring engineering costs and leadtimes involved in production of the brazing fixture. Plastic pin gridarray packages most commonly use pins which are inserted into metallizedthrough holes in a circuit board, while the dimensions of pins and theholes normally chosen to facilitate good contact between the walls ofthe pins and the coating of the holes. This approach has a disadvantagein that the coated holes and the pins block some circuit routingchannels within the circuit board, thus forcing either use of narrowcircuit traces, or increase in circuit board area, either of whichresults in increased costs.

[0003] Permanent connection of the pin grid array packages to circuitboards often is accomplished by inserting pins through correspondingholes in a circuit board, the pins protruding to a predetermined lengthbeyond the circuit board. A resulting assembly then is passed through awave soldering machine, and the pin grid array thus is soldered to thecircuit board. Alternatively, a pin grid array can be inserted into alow insertion force or zero insertion force socket for a demountableassembly. Such a socket, in its turn, normally is connected permanentlyto a board.

[0004] A current trend in interconnections is toward face-to-facesurface mounting of components to boards and semiconductor chips tosubstrates. This approach is best accomplished with protruding contactstructures on top of (or otherwise protruding from) contact carryingconductive terminals or traces. Conductive terminal arrangements onfacing components and substrates are increasingly being made of the areaarray type, as this allows for larger contact-to-contact separation ascompared with components characterized by peripheral arrangement ofinterconnection contacts.

[0005] Pins attached to either ceramic or plastic packages according tothe traditional methods are, in general, not appropriate for mounting topatterns of surface contacts on circuit boards, due to pin lengthvariation. For surface mounting, the pins would have to be planarized,which represents an additional expensive step subsequent to pinassembly. In addition, there is a significant cost penalty associatedwith production of pin-carrying packages with pin-to-pin separations of50 mils, or lower.

[0006] There is currently an increasing need for a low cost method ofattaching protruding contacts from conductive terminals, arising fromproliferation of surface mountable area array contact packages.Stand-off height of protruding contacts is particularly important whencoefficients of thermal expansion of components and of circuit boardmaterials differ significantly. The same is true for attachment ofun-packaged semiconductor chips to interconnection substrates. Theseexpansive concerns call for a low cost, high volume method ofmanufacturing protruding, controlled aspect ratio or shape electricalcontacts on top of (or otherwise protruding from) contact carryingconductive terminals, on top of any device or circuit bearing substrate,board material or component, and its applications to surface mountinterconnections of devices, components and substrates.

THE PRIOR ART

[0007] U.S. Pat. Nos. 5,189,507, 5,095,187 and 4,955,523 disclose amethod of manufacturing of controlled height protruding contacts in ashape of wires for direct soldering to a mating substrate. The wires arebonded to terminals without use of any material other than that of wireand the terminals, using ultrasonic wirebonding methods and equipment,which comprises a standard industry technique for interconnectingsemiconductor chips to packages. The patents also describe a bondinghead which incorporates a wire weakening means for controlling length offree standing severed wires. Vertically free standing wires present ahandling problem during assembly, which is addressed in the patents byproviding for polymer encapsulation of bonds between the wires andterminals. The polymer coating, which is optional, also compensates foranother disadvantage of the approach, namely weak points along the wire,typically the point of contact between the wire and terminalmetallization, and in case of ball bonding, in a heat effected zone ofthe wire just above impression of a bonding capillary. While thesepatents provide for controlled height contacts, and discuss 2 d to 20 daspect ratios, in practice they do not assume controlled aspect ratiosfor all kinds of protruding contacts which are required in variousapplications. For instance, standard, high speed wirebonding equipmentcould not handle a 30 mil diameter wire. Therefore, according to theseinventions, a 30 mil diameter, 100 mil high contact could only beproduced on lower throughput specialized equipment, at higher cost. Inaddition, a gold wire as described in a preferred embodiment, would havea problem of dissolving in solder during a soldering cycle, which causeslong term reliability problems with solder joints. Similarly, directsoldering of copper contacts would in many cases result in undesirablereaction between copper and solder at elevated temperatures. Whilenickel metal is the material of choice for solder joint reliability,nickel wire can not be used for ultrasonic wirebonding to metalterminals due to its high mechanical strength and passivating, oxideforming properties. Chemical, physical and mechanical properties, aswell as permissible dimensions and shapes of the protuberant contactsproduced according to this invention are limited to the capabilities andmaterials choices compatible with known wire bonding techniques.

[0008] U.S. Pat. No. 3.373,481 describes a method of interconnectingsemiconductor components on substrates by means of dissolving protrudinggold projections on the components in solder masses formed on thesubstrate terminals. The gold projections are formed by compression andextrusion of gold balls against the terminals. This approach isincapable of producing high aspect ratio protruding contacts because oflimitations of the extrusion method. In addition, dissolution of gold insolder, as taught by this approach creates a problem due to reliabilityconcerns. The method also limits selection of contact material to easilyextrudable metals, like gold.

[0009] There are several methods in the prior art for controlledelongation of solder masses between a component and a substrate. Thegoal is to create a column-like solder shape, preferably an hourglassshape, in order to achieve increased resistance to thermal cycling. Tothat end, U.S. Pat. No. 5,148,968 discloses a web-like device which uponheating during solder reflow stretches the solder connections, formingsuch hourglass shaped solder columns. Aspect ratios of the columns aredetermined by the mass of solder in the joint, dimensions of the solderwettable terminals on the substrate and the component, and by thecharacteristics of the stretch device. This method is only limited tocontact materials which are reflowed during the assembly, and requiresexternal hardware for forming the contact shape, which adds cost of thehardware and increases the process complexity.

[0010] U.S. Pat. No. 4,878,611 teaches formation of controlled geometrysolder joints by applying controlled volumes of solder to asemiconductor package and a substrate, bringing solder masses incontact, and reflowing the solder masses while maintaining controlledseparation between the component and the substrate through mechanicalmeans. This approach also requires hardware means for maintaininglongitudinal dimension of the contacts, and does not lend itself tostandard practices of surface mount soldering, in which industry alreadyhas made substantial time and capital investments.

[0011] In the same spirit, U.S. Pat. No. 4,545,610 discloses a processfor forming elongated solder joints between a plurality of solderwettable terminals on a semiconductor component and a substrate by meansof solder extenders, which transform the shape of the solder joints intouniform hourglass shapes during a solder reflow step. This approachrequires additional, non-standard processing of either a silicon device,or on a substrate, which includes attachment of reflowable solderextenders, and non-reflowable means of maintaining vertical spacingbetween the silicon device and the substrate.

[0012] U.S. Pat. No. 5,154,341 discloses the use of a spacer bump whichis composed of a solder alloy which does not melt at the temperature ofcomponent soldering. A eutectic solder microball is placed on a contact,and upon the reflow the reflowable solder encases the non-reflowablespacer, and produces an hourglass shaped joint. The aspect ratios of thejoint contacts are controlled by dimensions of the spacer.

[0013] U.S. Pat. No. 4,332,341 teaches solid state bonding of solderpreforms to components, substrates or both, for further joining.Resulting protruding solder contacts either collapse during soldering ifthey consist of eutectic solder, or do not reflow at all, when theyconsist of higher melting temperature solder. In the latter case, acomponent would not have the benefit of a self-alignment effect as thepool of solder is confined to the vicinity of the terminals, and a mainportion of the joint which controls aspect ratio, does not melt.

[0014] U.S. Pat. No. 4,914,814 discloses a process for fabricatingsolder columns through use of a mold with an array of pin holes, whichare filled with solder, brought into contact with terminals on acomponent, and bonded by melting the solder which wets the terminals.The component with columns is then bonded to a substrate through reflowin a solder with lower melting temperature than the solder of thecolumns. This approach requires generating a mold for each solder columnarray pattern, commonly involving undesirable non-recurring engineeringexpenses and associated increase in delivery times.

[0015] U.S. Pat. No. 3,509,270 discloses a printed circuit assemblywhich is interconnected with a dielectric carrier that has a pluralityof spring elements positioned in its apertures, the springs areoptionally encased in a solder material to facilitate permanentelectrical contact between circuit elements. This approach requires acustom interposer pattern manufactured for each application, whilesolder coated springs would have to be placed individually inside theapertures. Additionally, soldering usually requires flux, while theinterposer material makes it difficult to clean flux after the reflowprocess.

[0016] U.S. Pat. Nos. 4,664,309 and 4,705,205 disclose a device and amethod for interconnection with reinforced solder preforms which use aretaining member provided with apertures. The retaining member isoptionally dissolved to leave resilient interconnect structures. Thesolder columns maintain their shape in the molten state, supported byparticles, filaments, spiral metallic wire or tape. 20 to 80% by weightof filler material is specified. This approach, as several of the abovedescribed approaches, requires a custom made retaining member for everyinterconnect application, and therefore requires an additionalnon-recurring engineering expense and increased delivery time for everyproduction order.

[0017] U.S. Pat. No. 4,642,889 teaches use of an interposer with aplurality of interconnect areas, interconnect areas comprise wire meanssurrounded with solder, and incorporate a soldering flux material. Uponheating the solder reflows and connects to the terminals of the matingcomponents and boards, while the wires in the middle of each solderjoint insure a column-like joint shape. The interposer preferably isdissolved away. While providing means for controlled aspect ratiointerconnect joints, this approach also requires use of a custommanufactured interposer and inevitable non-recurring engineeringexpenses and increased delivery times. In addition, when improvedalignment of the interconnect to the terminals is required, asterminal-to-terminal distances decrease, this approach suffers from heatand environmental effects on interposer material, causing it to distortor change dimension during processing steps, which makes the alignmentdifficult, and limits this approach to relatively coarseterminal-to-terminal pitch applications.

[0018] An elongated protruding solder contact is taught according toU.S. Pat. No. 5,130,779, by sequentially encapsulating solder depositswith a barrier metal. This approach insures that a staged solder depositdoes not collapse upon reflow, and a controlled aspect ratio soldercontact is thus formed. In order for the barrier metal to be effective,the walls of sequentially deposited solder masses must have a slope.Deposition of such a structure of solder is a lengthy and expensiveprocess.

[0019] A method of attaching highly compliant leads to an array matrixof contacts on a semiconductor package is disclosed in U.S. Pat. No.4,751,199. An array of leads is manufactured according to the requiredpattern with temporary tab structures tying the leads together.Compliant leads are gang bonded to terminals on the semiconductorpackage, and tabs are removed leaving compliant protruding contactleads, ready for attachment to a substrate. This approach, like theinterposer techniques described above, requires specific tooling forevery new package with a distinct pattern of the array of contacts.

OBJECTS AND SUMMARY OF THE INVENTION

[0020] One object of the present invention is to provide a high volume,low cost manufacturing process for production of precise shape andgeometry protuberant conductive contacts on a wide variety of electroniccomponents, the contacts having a controlled set of physical,metallurgical and mechanical properties, bulk and surface. Suchprotuberant contacts can be employed to satisfy electrical, thermal orgeometrical requirements in various aspects of electronicinterconnection applications. An inventive, multiple stage process isprovided, according to which, first, wire stems are bonded to contactcarrying terminals, the stems being shaped in three dimensional space,to define skeletons of the resulting contacts. The conductive contactsare then completed through at least one deposition step of a coatingwhich envelopes or jackets the wire skeletons and the terminals. Thecommon coating not only helps to “anchor” protruding contacts to theterminals, but also provides for characteristics of the protuberantcontacts with respect to long term stability of their engagement contactwith mating electronic component, including but not limited tointerconnection substrates, semiconductor devices, interconnect or testsockets. The coating also determines soldering assembly characteristics,as well as long term effects from contact with solder. The coating,along with the wire material properties, determines the mechanicalcharacteristics of the resulting protuberant contact. The wire serves asa “skeleton” of a resulting protruding contact, and the coating servesas its “muscle”.

[0021] The wire skeleton can be bonded employing high productivity,highly automated ultrasonic, thermosonic and thermocompressionwirebonding equipment (hereinafter referred to as ultrasonic wirebondingequipment). The wirebonding equipment can be organized for ball bondingtype ultrasonic wirebonding process, typically used for gold or copperwirebonding, but modifiable for use with other types of single phase ornoble metal coated wires. Wire skeletons consisting of free standingsingle or multiple wire stems can be produced. As required by the shapeand dimensions of the resulting conductive contacts, the stems can bestanding normal to a terminal or at an angle thereto, or can be formedin three dimensional space. Alternatively, wire skeletons produced usingan ultrasonic ball bonder can be produced by forming a traditionalwire-bonding loop, which originates and terminates on a contact carryingterminal, or which originates on the contact carrying terminal andterminates on a sacrificial conductor outside the terminal area. Thenthe sacrificial conductor is selectively dissolved away after completionof the contact processing. Optionally, a wedge bonding type ultrasonicwirebonder can be employed, in which case controlled shape loops of wireare formed with both ends of a loop on the same terminal, or they areformed by originating the loops within the area of the terminal andterminating or severing the loops outside the terminals. Both types ofwirebonders are available commercially from a variety of suppliers, andare highly automated, with the bonding speeds exceeding 10 wires persecond.

[0022] An additional object of the present invention is to produce arraypatterns of contacts for unique component designs, without incurringcosts and delays associated with production of unique tooling. Thisobject is achieved through use of a sequential wirebonding process forattaching of the wire skeletons to the terminals, and then overcoatingthem in a single, non-pattern-specific step. Location targeting andgeometric characteristics are entered into an electronic control systemof the wirebonding equipment with a specific set of commands. A programcontrols all aspects of wire forming and shaping process, as well asbond characteristics. Production of the multiple protruding contactsdoes not require time-limiting and costly production of molds, masks orthe like, which otherwise would be specific to every incoming order.This object is exemplified by application of the present invention toproduction of integrated pin-shaped contacts for ceramic pin grid arraypackages. This is achieved by bonding straight vertical, single stemskeletons, perpendicular to the surface of terminals, and overcoatingthem with a conductive structural metal or alloy, consistingsubstantially of nickel, copper, cobalt, iron or alloys thereof, withthe thickness of the deposit determined by the required pin diametervalue. This can also be accomplished with equal ease on plastic pincarrying substrates.

[0023] Yet another object of the present invention is to createprotruding, tower-like solder contacts which substantially maintain awell controlled aspect ratio even when the solder is molten. This objectis achieved through first bonding a wire skeleton which will define thefinal shape and aspect ratio of a solder contact, then optionallyovercoating it with a barrier layer which prevents long term reactionbetween the solder and the wire, and finally depositing a mass of solderwhich wets the skeleton with a barrier, and clings onto the skeletoneven after multiple reflows.

[0024] Yet another object of the present invention is to createcontrolled shape resilient contacts on top of (or otherwise protrudingfrom) contact carrying terminals arranged in various patterns, includingarrays. This object is achieved by overcoating the wire skeleton with atleast one coating having a predetermined combination of thickness, yieldstrength and elastic modulus to insure predetermined force-to-deflectioncharacteristics of resulting spring contacts.

[0025] Yet another object of the present invention is to produceprotruding contacts on top of (or otherwise protruding from) a multitudeof contact-carrying terminals, where the terminals have varying verticalcoordinates, corresponding to an origin point of the protrudingcontacts, while uppermost points of the protruding contacts extend to avertical coordinate which is substantially identical, within apermissible tolerance level for the component or substrate which is tobe subsequently connected to the contacts. In a different embodimentrelated to this object, the terminals can originate on variouselectronic components, while the protuberant contacts extend to asubstantially identical vertical coordinate. This object is achieved bycontrolling a wire severing step, by always severing the wire at apredetermined vertical coordinate. Overcoatings then follow the skeletonwire shape and geometry, yielding a contact having a controlled verticalcoordinate level, regardless of the Z-axis point of origination of thecontact, e.g. plane of the terminal. Some of the terminals havingvarying Z-coordinates and overlying the component, can optionally andadditionally overlie single or multiple electronic devices, placed onthe electronic component. In another embodiment related to this objectof the present invention, the vertical coordinate of the tips of theprotuberant contacts can be controlled by the software algorithm of theappropriately arranged automated wirebonding equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The foregoing and other objects and advantages will appear morefully from a Summary of the Invention which follows viewed inconjunction with drawings which accompany and form part of thisApplication. In the drawings:

[0027]FIGS. 1a and 1 b are schematic representations of a knownball-and-wedge technique to form a loop-like wire skeleton of aprotruding electrical contact.

[0028]FIG. 2 is a cross-sectional representation of a conductive contactresulting after overcoating the wire skeleton depicted in FIG. 2.

[0029]FIG. 3 is a schematic representation of a conductive contacts withskeletons consisting of two loop-like stems.

[0030]FIG. 4 is a cross-sectional representation of protruding soldercontacts based on loop-like skeletons with a barrier metal between thewire material and the solder.

[0031]FIG. 5 is a schematic representation of protruding solder contactswhere each skeleton consists of two loop-like stems, the skeletonmaterial overcoated with a barrier layer prior to deposition of solder.

[0032]FIGS. 6a, 6 b and 6 c depict a sequence of bonding one end of aloop-like stem to a sacrificial pad, overcoating the skeleton, and afollowing step of removal of a sacrificial pad, resulting in protuberantcontact with a floating end.

[0033]FIGS. 7a, 7 b and 7 c represent schematically a sequence ofbonding single stem, perpendicular skeletons to contact-carryingterminals.

[0034]FIG. 8 is a cross-sectional view of vertical protuberant contactsproduced by overcoating the skeletons depicted in FIG. 7c.

[0035]FIGS. 9 and 10 schematically represent an example of the skeletonsbased on two single stems perpendicular to the plane of contact carryingterminals, and the protuberant contacts resulting after overcoatingskeletons shown in FIG. 9 with contact material.

[0036]FIG. 11 is a schematic representation of protuberant contactsoriginating on terminals lying in different planes, and with tips of thecontacts lying in a common horizontal plane.

[0037]FIG. 12 is a schematic representation of protuberant contactsoriginating on terminals lying two distinct electronic components, andwith tips of the contacts lying in a common horizontal plane.

[0038]FIG. 13 is a schematic representation of a solder protuberantcontact based on a double-stem skeleton, with a barrier layer betweenthe skeleton and the solder.

[0039]FIG. 14 is a schematic of S-shaped wire skeletons.

[0040]FIG. 15 is a cross-sectional representation of resilientprotuberant contacts resulting after overcoating the S-shaped skeletonswith an appropriate conductive material.

[0041]FIG. 16 is a cross-sectional representation of resilientprotuberant contacts with microprotrusions for improved contactcharacteristics.

[0042]FIG. 17 is a representation of a fence-like skeleton on top of acontact-carrying terminal.

[0043]FIG. 18 is a cross-sectional representation of a pin grid arraypackage incorporating pins produced according to the method of thepresent invention.

[0044]FIG. 19 is a schematic representation of an assembly of asemiconductor package incorporating protuberant solder contacts and aninterconnection substrate, after completion of the solder reflow step.

[0045]FIG. 20 is a schematic representation of an electronic package,incorporating protuberant solder contacts on its two interconnectionsurfaces.

[0046]FIG. 21 is a schematic representation of a dielectric interposerwith resilient protuberant contacts on its two surfaces, the interposerincluding means of electrical interconnection between the two surfaces.

DETAILED DESCRIPTION OF THE INVENTION

[0047] The method of the present invention relies on wirebondingequipment to produce controlled aspect ratio and shape wire skeletons,which are subsequently overcoated with a desired material in order toproduce a required set of properties for protuberant electricalcontacts. FIGS. 1A and 1B depict use of a ball-and-wedge wirebondingmachine to form a wire skeleton. More detailed descriptions of this andwedge-wedge wirebonding methods, commonly used in the semiconductorindustry for interconnecting silicon devices to packages, can be foundin Electronic Packaging and Interconnection Handbook edited by CharlesA. Harper, on pp. 6.62-6.64 and 7.28-7.30. FIG. 1A illustrates acapillary 1, with an open clamp 2, containing an end portion of acontinuous wire 20 with a ball 21 formed at its feed end below thecapillary tip. The ball 21 is brought in contact with a contact carryingterminal 90 on top of (or otherwise contained within) a substrate 10. Asa result of application of pressure, temperature or ultrasonic energy,or combinations thereof, a ball is bonded to the terminal. The ball 21in FIG. 1A is in the bonding process changed into ball bond 22 shown inFIG. 1B. Subsequent capillary motion sets the shape of a wire stem 60.Loop geometry of the wire stem is controlled by parameter settings inthe software control algorithm of the wirebonding equipment. A secondend of the wire stem is bonded to the terminal 90 by means of pressure,temperature or ultrasonic energy, and deforming the wire against theterminal 90. A wedge-shaped joint 23 thereby is produced. The capillarythen rises to a predetermined height, a clamp 2 closes, and the wire issevered at a thinnest point of the joint 23, leaving a fractured freeend 24 below the capillary 1. In preparation for forming a next joint, anext ball 21 is formed at the severed free end 24 of the of the wireunderneath the capillary, and the cycle is repeated. The loop-shapedstems can be alternatively produced by wedge-wedge technique, where bothend of the stem are bonded by the wedge tool. Wire material forball-wedge and wedge-wedge type of wire-bonding is most commonly gold,aluminum or copper, with slight modifications by other elements, likeberyllium, cadmium, silicon and magnesium to control the properties.other materials, including solder, and specifically lead-tin solderwire, have been employed. Alloys of silver and platinum group elementscan also be used for wire material. Gold, aluminum and copper, or alloysbased on these metals, are the preferred wire materials. The terminalmaterial should preferably use at least a top layer (if a multi-layerstructure) of gold or aluminum, but numerous other metallizations can besuccessfully used, requiring different levels of ultrasonic vibration,force and temperature. A modern automated wirebonder is capable ofbonding over 10 loop-shaped stems per second.

[0048] In the embodiment of the present invention represented in FIGS.1A and 1B, a wire skeleton 30 is formed upon severing the single wirestem 60. As shown in FIG. 2, the skeleton 30 geometrically defines theprotuberant contact produced by the method of the present invention.

[0049] Referring now to FIG. 2, physical, finishing and determiningmechanical and chemical properties of the resulting protuberant contact50 are provided through overcoating of the skeleton 30 and the contactcarrying terminal 90 with a continuous coating 40, which consists of atleast one electrically conducting layer. The continuous coating 40anchors the skeleton to the terminal by bridging in the areas of contactbetween the ball bond 22 and wedge bond 23 and the terminal. Theovercoating material may be significantly stronger than the skeletonmaterial. It can be applied by wet electrochemical means, e.g. throughelectrolytic or electroless aqueous solution plating of metals on theskeleton and the terminal. The wet plating techniques are, for instance,described in Metal Finishing Guidebook annually published by Metals andPlastics Publications, Inc. One preferred embodiment compriseselectroplating of nickel out of nickel and its alloys. This method iscapable of depositing controlled thickness coating with a tensilestrength in excess of 80,000 pounds per square inch. Additionalimprovement of mechanical strength of the resulting contact is achievedwhen a coating with a compressive internal stress is deposited, whicheffectively increases the stress level required to deform or break aresulting protuberant electrical contact.

[0050] The coating method also optionally includes so-called physicaland chemical vapor methods of conductor material deposition. Theseoptional techniques are detailed in a book by M. Ohring, The MaterialsScience of Thin Films, Academic Press, 1992. Coating methods alsoinclude and contemplate deposition of conductors through variousdecomposition processes of gaseous, liquid or solid precursors.

[0051] Nickel has a strong tendency to form an oxide and is therefore,not the best choice as a contact metal. It requires large contact forcesto break through the oxide. For low contact force applications, itrequires a second noble or semi-noble coating layer on top. Gold,silver, elements of the platinum group and their alloys are preferredchoices as a noble or semi-noble overcoating layer. Similarly, in otherinstances, multiple layers, comprising conductive overcoating 40, can beselected to tailor the set of properties of the protuberant contact to agiven application.

[0052] Within the method of the present invention, a plurality of wirestems can be employed to create a wire skeleton. Referring now to FIG.3, two wire stems 60 comprise each skeleton 31. Conductive overcoating40 completes protuberant contact 51.

[0053] In a growing number of applications there is a requirement forcontrolled aspect ratio columns of solder on top of an area array ofterminals on ceramic and plastic semiconductor packages. Most often, anarea array of balls made of a solder alloy, commonly a eutectic alloy oflead and tin, is used in surface mounting of components with an array ofterminals to a matching array of contacts on a circuit board. Long termresistance of such solder contacts is determined by the height, shapeand the material characteristics of the solder joints. The method of thepresent invention provides for controlled shape solder contacts formedaround a wire skeleton. Referring now to FIG. 4, wire skeletons 30 arefirst coated with an optional barrier layer 41, and in the followingstep are overcoated by a solder mass 42. The barrier layer 41 inhibitsan undesired reaction between the wire material and the solder mass.This barrier layer is especially important in the embodiment of theinvention providing for gold wire skeletons and a solder mass comprisingan alloy of lead and tin. Due to reactivity between gold and tin, anddetrimental effects of intermetallic, gold-tin compounds on the serviceperformance of solder joints, the reaction between gold and tin must beprevented. A 100 to 1,000 microinch barrier of a nickel alloy istypically a sufficient deterrent to the reaction between solder and goldfor most applications.

[0054] Deposition of solder overcoating can be accomplished, forexample, by sending a package or a substrate through a solder waveprocess cycle in a solder wave equipment. The solder wets the barrierlayer 41, and bridges among adjacent wire portions forming theloop-shaped stems, to assume a shape depicted in FIG. 4. The shape doesnot substantially change during subsequent reflow cycles, as long asthere is no significant reaction between the solder and the barriercoating. The overall shape of the solder column depends on area of theterminal and geometry of the skeleton. Bridging by molten solder massesbetween the ascending and descending branches of loop-shaped stems, andthe surface of the terminal, enables the skeletons to contain andsupport disproportionately large volumes of solder. A preferred solderprotuberant contact produced by the method of the present invention willcontain more than 70 volume percent of solder, and more preferably over80 volume percent of solder by volume, with the remainder comprising theskeleton and the barrier material.

[0055] A preferred embodiment for a solder column contact, depicted inFIG. 4, is a gold based alloy wire loop skeleton 30, with a nickel basedcoating 41, and a near eutectic lead-tin solder mass 42. The gold wirediameter usually ranges between 0.0005 and 0.005 inches, and preferablybetween 0.0007 and 0.003 inches. The nickel overcoat 40 usually rangesin thickness between 0.00005 and 0.007 inches, and preferably between0.000100 and 0.003 inches. Another preferred embodiment is a copperalloy wire skeleton, which can be directly overcoated with solder mass.In another preferred embodiment, copper based wire skeleton is firstovercoated with a nickel based barrier layer, followed by deposition ofthe solder material.

[0056] Both types of protuberant contacts, solder contacts 52 shown inFIG. 4, and contacts 50 shown in FIG. 2, can be soldered to aninterconnection substrate or a component using surface mount solderingtechnology. Solder contacts 52 have an advantage in handling prior toprocessing, in that solid solder mass 42, FIG. 4, bridging between thewire branches of the skeleton and surface of the terminal, makes thecontact more resistant to mechanical damage in handling, e.g. bendingand breakage.

[0057] Further increase of the overall proportion of solder material inprotuberant solder contacts can be achieved by using multiple wire stemskeletons. Referring now to FIG. 5, two severed stems 60 comprise eachskeleton 31 bonded to a contact carrying terminal 90. An optionalbarrier material 41 is first deposited on top of the terminal 90 and theskeleton 31, in order to inhibit a possible reaction between the solderand the skeleton material. A solder material 42 completes theconstruction of a protuberant solder contact. By presenting moreascending and descending wire branches for solder bridging, the relativevolume content of solder material in the protuberant contact can besignificantly increased.

[0058] Protuberant solder contacts 52 and 53 in FIG. 4 and FIG. 5,substantially retain their shape even during subsequent solder reflows,due to strong wetting between the solder and the barrier layer 41. Thisshape retention is despite solder constituting preferably more than 70volume percent of the protuberant contacts 52 and 53, and mostpreferably more than 80 volume percent. This property of protuberantsolder contacts produced by the method of the present invention allowsfor contacts to be put on electronic components prior to device assemblysteps, even if the assembly process involves heating the component 10above the melting temperature of solder material 42.

[0059] In the spirit of the present invention, but in yet an alternateembodiment, either the ball or a wedge bond of the wire stem can beformed outside the area of a contact carrying terminal. As shown in FIG.6A, a wedge bond 29 completes a wire stem 61, and upon the severing stepat the bond 29, resulting in formation of a wire skeleton 32. The wedgebond 29 is formed outside the area of the terminal 90 at a terminal 91.The terminal 91 is positioned on top of a sacrificial layer 80, or couldoptionally be sacrificial by being comprised of a dissimilar metal fromthat of terminal 90. In both cases, the sacrificial arrangement istemporarily used for electrical contact to an electrode, in that it isrequired for electroplating of a conductive coating 43, enveloping theskeletons 32 and the terminals 90 and 91, to complete protuberantconductive contacts 54, as illustrated in FIG. 6B. The sacrificial layeris also used for assuring a different Z-axis coordinate for the bonds 22and 29. As illustrated in FIG. 6C after a coating deposition and aremoval step for the sacrificial layer, one of the ends of the wire loopbased contact ends up being suspended above the substrate 10. Thissuspension is especially important for formation of controlled geometryspring contacts, capable of resiliently engaging with mating terminalson a component or a substrate for testing, burn-in or demountableelectrical interconnect in service. The variation of the Z-coordinate ofan end of the wire-loop shaped contact allows for resilient Z-axismovement of a tip of the resulting spring when a force is appliedthereto.

[0060] Referring now to FIGS. 7A through 8, another preferred embodimentof the method for manufacturing controlled aspect ratio protuberantcontacts. In this embodiment, only ball bonding is used, the wires arebonded substantially vertically. The software of the control system ofthe wirebonder is programmed to exclude the common wedge bonding stepfor severing the wires. Instead the same electronic or hydrogenflame-off used for ball formation prior to the ball bonding is employedto severe the wires at a predetermined height. FIG. 7A depicts a ballbonding capillary 1, wire 20 after the first ball bonding step whichcreated a ball bond 22 on top of contact carrying terminal 11. After thebond the capillary moves up to a predetermined position, and electrode 3is brought under a high potential, resulting in a generation of a sparkwhich melts and severe the wire 20 at a predetermined spot, asillustrated in FIG. 7B. As a result of the severing step a wire skeleton33 is created, which comprises a single stem 62 extending to its severedend 25. The severing step also readies the feed end 21 of the wire 20 tothe next stem bonding step.

[0061] After vertical wire stems 62 are formed on contact carryingterminals 90, and after the severing step which defines single stemskeletons 33, as shown in FIG. 7C, the wire skeletons 33 and the contactcarrying terminals 90 are overcoated with a deposit 44, originating atthe terminals and extending to the tops of the wires as a continuousblanket coating, to complete protuberant contacts 55. As in the previousembodiments, the composition and the thickness of the continuous coatingis selected to satisfy requirements of a given application.

[0062] The protuberant vertical contacts 55 shown in FIG. 8 areespecially useful as a replacement method for standard techniques forattachment of pins to plastic and ceramic semiconductor packages, amethod which results in lower package cost and reduced pinned packageproduction time. This usefulness is due to the fact that the pin-shapedcontacts produced by the method of the present invention do not requirepattern specific tooling or molds.

[0063] Thickness and material composition of conductive layer 44 shownin FIG. 8 depends on the production, assembly and service requirement,and the characteristics of package material. The layer 44 can comprisenickel alloy. In another embodiment layer 44 can comprise a copperalloy. Yet in another embodiment layer 44 can comprise alloys of nickel,iron and cobalt, with controlled thermal expansion characteristics. Inyet additional embodiment, layer 44 is formed through multipledeposition steps, the top deposit comprising a noble or semi-noble metalor alloy, out of a group of gold, platinum, silver, rhodium, rutheniumand copper. The top deposit improves electrical contact characteristicsof the pin-like contact 55.

[0064]FIGS. 9 and 10 illustrate the process of attachment of contacts 56to the contact carrying terminals 90. The contacts are based onskeletons 34, each skeleton 34 comprising two vertical wire stems 62.The skeletons and the terminals 90 are overcoated by layer 44 tocomplete protuberant, vertical-double-stem contacts 56. This type ofcontacts can be useful in soldering, where multiple branches of thecontact present themselves to solder for improved assembly yield.

[0065] Referring again to FIG. 7b, due to the stationary position of theelectrode 3, the wire 20 always gets severed at a predeterminedelevation, regardless the Z-coordinate of the ball bond 22. Uniformelevation is a very desirable property, especially in cases whencontacts are placed on a substrate or a component which is not planardue to manufacturing tolerances, or is warped during thermal assembly orprocessing steps. In other instances, various terminals 90 on anelectronic component 10 are provided in different planes, as illustratedin FIG. 11, while the highest elevation points of the protuberantcontacts 56 may be required to lie in a substantially identicalhorizontal plane. This configuration is especially important whencontact carrying terminals lie at different positions of aninterconnection substrate, but they bear protuberant contacts which mustcontact a highly planar device or component. This self-planarizingcapability of the method of the present invention is also important whenthe terminals lie on different components, but the tips of protuberantcontacts must terminate in a substantially identical horizontal plane.As illustrated in FIG. 12, terminals 90 and 92 lie on components 10 and11 respectively, while the protuberant contacts 56 vertically terminatein a substantially identical plane. In the embodiment depicted in FIG.12, the two components, 10 and 11, are optionally interconnectedelectrically by means of conductive masses 900. In this embodiment ofthe invention, component 11 can represent an interconnection substrate,while one or a plurality of components 11 can represent passive devices,like capacitors or resistors. The protuberant contacts may serve forinterconnection of a bare, unpackaged semiconductor device (not shown inthe FIG. 12) to the interconnection substrate 10. Such an electricalarrangement decreases the inductance value between critical contacts onthe semiconductor device and a capacitor component, which improveselectrical performance of semiconductor devices operating at highfrequencies.

[0066] Wire skeletons consisting of multiple vertical wire stems areespecially useful for protuberant solder contact applications. FIG. 13illustrates a cross section of a protuberant solder contact 57 supportedby a wire skeleton 34 consisting of two vertical stems 62. An optionalbarrier layer 45 is first deposited, followed by the solder 42deposition step. The deposition step can be accomplished by passing asubstrate with protuberant skeletons 34, overcoated with a barrier metal45, through a common wave soldering machine. The solder bridges betweenthe wires, in addition to coating the outsides and top surfaces of thewires due to wetting. In contrast, a single wire skeleton would supportsolder only through the wetting mechanism, without a possibility ofbridging, and would support less bulk solder per wire as a result ofsolder application by solder wave technique. A common solderstate-of-the-art wave soldering method is described in ElectronicMaterials Handbook, Volume 1 Packaging, from ASM International,Materials Park, Ohio, on pp. 688 through 696. A preferred method forproducing this embodiment of the present invention involves use ofmultiple gold wires, ranging from 0.0005 to 0.005 inches in diameter,and more preferably 0.0007 to 0.003 inches in diameter, overcoated with0.000030 to 0.005 inches of nickel or nickel alloy or cobalt or cobaltalloy, and more preferably with 0.000050 to 0.003 inches of nickel ornickel alloy. The amount of solder deposited from solder wave woulddepend on the wave conditions and the dimension of the overcoatedskeleton, as well as the size of the contact carrying terminal.

[0067] In another embodiment of the present invention, the solderovercoat 42, which completes a protuberant solder contact 57, is acontinuous coating deposited over a wire skeleton without a barrierlayer between the solder and the wire and terminals. Gold wire without abarrier is not an appropriate choice for this embodiment, because acontinuous reaction between the solder and the gold embrittles thesolder or solder joint to a substrate or to a component. However, acopper wire is useful to form the wire skeleton, and then a soldercoating is applied using, for example, a solder wave approach referredto above.

[0068] An alternative approach to forming solder columns on top of wireskeletons is to plate electrolytically the solder. The electrolyticallydeposited solder is appropriate for standard surface mount assembly.Alternatively, the solder can be reflowed after electrolytic deposition,and prior to the assembly.

[0069] The method of forming wire skeletons described by means of ballbonding, shown in FIGS. 7A through 7C is appropriate for formingindividual resilient contacts. Instead of forming vertical wires, theskeleton wires for spring contacts are formed with the shape whichdeviates from vertical. One preferred embodiment for forming springcontacts is illustrated in FIGS. 14 and 15. A single or multiple wire isball bonded to a terminal, followed by a motion of the capillary whichforms the wire into an S-shaped wire stem 63. The forming step isfollowed by a severing step performed by means of an electronicflame-off provided by the tool 3. The severing step defines a skeletonconsisting of single or multiple S-shaped wire stems. The skeletons 35and the resilient contact carrying terminals 90 are then overcoated by aconductive deposit 46, which possesses mechanical characteristics,which, along with the s-shape of the stems, ensures a resilient responseof the resulting protuberant contacts 58 to a deflective force.

[0070] One preferred embodiment for a resilient overcoating is a nickelor a nickel alloy layer. For example, Ni electroplated out of standardnickel sulfamate solution could be used. Such nickel deposit can beproduced with compressive internal stress which would improve the springcharacteristics, as well as varying strength and ductility levels. Aplated nickel-cobalt alloy has greater strength and improved resilientproperties. Rhodium, ruthenium or other elements of the platinum groupand their alloys with gold, silver and copper constitute another groupof preferred embodiment overcoat materials. Tungsten or nickel can alsobe deposited by chemical vapor deposition techniques, and representanother preferred embodiment materials.

[0071] Gold is the most commonly used wire material for ultrasonicwirebonding applications, but it is soft and it may not be anappropriate skeleton material for a spring contact if it constitutes asignificant portion of the spring cross-sectional area. One embodimentof the present invention provides for a common high speed bonding ofgold skeleton wires. An alloying layer is then deposited, which whenreacted with gold, forms a gold alloy, the alloy having higher strengththen pure gold. One preferred embodiment provides for deposition of tinon top of gold wire, with subsequent reaction of gold and tin at atemperature below the melting temperature of gold-tin eutectic. Agold-tin alloy results, which is significantly stronger than gold.

[0072] The contact properties of the springs in FIG. 15 can be enhancedby overcoating the spring material with a noble or semi-noble material,like gold, silver, or elements of the platinum group and their alloys.This overcoating reduces contact resistance of spring contacts 58 whenthey are engaged against the mating conductive terminals forinterconnection purposes. Another embodiment is depicted in FIG. 16,with a spring coating 47 having local protrusions. Such a coating can becreated through dendritic growth of an electroplated deposit, or throughincorporation of foreign particulates into the conductive deposit 47.Alternatively, a regular uniform first deposit layer can be applied,which provides for resilient properties, and the subsequently depositedtop layer incorporates local protrusions or particulates to completeconductive deposit 47. The local protrusions dramatically increase thelocal pressures exerted by the resilient protruding contact 59 onto amating terminal during the interconnection engagement, and reducecontact resistance when contacting easily passivating, oxide formingmaterials overlying the engaged terminals.

[0073] Resilient protuberant contact produced by the method of thepresent invention rely on the shape of a skeleton and the properties ofthe conductive material for its spring properties. In another embodimentof the present invention, wire stems or wire skeletons can beadditionally shaped by a tool external to a wirebonding equipment, prioror before the deposition step.

[0074]FIG. 17 illustrates another embodiment of the present invention,where a fence-like skeleton 36 is erected on top of a contact carryingterminal 90. The skeleton is formed by sequential bonding of theadditional loop-shaped wire stems, without the severing steps betweenthe bonds, until the skeleton is completed. This skeleton shape isespecially useful when large masses of solder have to be containedwithin the spagial boundaries determined by the skeleton 36. Onepreferred application of this embodiment is production of massive solderpads for thermal interconnection to heat sinks or substrates.

[0075] Protuberant contacts, as manufactured according to the presentinvention, are mounted on terminals on top of various interconnectionsubstrates; such as laminate printed circuit boards, Teflon basedcircuit boards, multi-layer ceramic substrates, silicon basedsubstrates, varieties of hybrid substrates, and other substrates forintegration of electronic systems known to those skilled in the art. Thecontacts can also be put on top of terminals directly on semiconductordevices, such as silicon and gallium arsenide devices, for subsequentdemountable or permanent attachment to interconnection substrates. Thecontacts could also be put on terminals on one or both sides ofelectronic components or devices, such as ceramic and plastic packageshousing semiconductor components, and other devices. The contacts couldbe put directly on top of passive devices, such as resistors andcapacitors.

[0076] One arrangement is shown in FIG. 18, wherein pin-like contacts 55are mounted to terminals of a ceramic semiconductor package 100. Asemiconductor device 101 is bonded to the package using die attachmaterial 112. Electrical interconnection of the device to the package isaccomplished with industry standard gold wire bonds 113, extending fromterminals 95 on the semiconductor device 101 to terminals 94 on theceramic package 100. This could alternatively be accomplished withaluminum wire wedge bonding. Interconnectivity within the ceramicpackage 100, between the wirebond terminals 94 and pin contact carryingterminals 96, is accomplished through the incorporation of conductors910 within the ceramic package body. The device is sealed hermeticallyin a package cavity with, typically, a Kovar alloy lid 111. The contactscan be put on before or after attachment and assembly of thesemiconductor device 101 in the package 100. The package 100 with theprotruding contacts is ready for interconnection to an interconnectionsubstrate, such as a printed circuit board. Depending on the method ofconnection, top deposit layer of the contacts 55 can be gold, noble orsemi-noble material, tin, or a tin-lead solder alloy.

[0077]FIG. 19 illustrates a cross section of a semiconductor package100, with semiconductor device 101 interconnected therewith, andinterconnected to a substrate 12 with terminals 97, the pattern of theterminals 97 matching the pattern of contact carrying terminals 96 onthe package 100. The package solder column shaped joints between theterminals 96 and 97 resulted after solder attachment of the package 100with columns 57 to a substrate 12. The surface mount soldering isaccomplished preferably by stencil or screen printing solder pastevolumes on top of each terminal 97, positioning contacts 57 in contactwith said solder paste, reflowing the solder in an oven at a temperatureabove the melting temperature of the solder in solder paste.Alternatively solder can be applied by various means of deposition, andplacement and reflow methods can be utilized. The soldering processfollows industry standard procedure commonly referred to asSurface-Mount Technology, and described in Chapter 9 of ElectronicPackaging and Interconnection Handbook, edited by Charles A. Harper, andpublished by McGraw-Hill, Inc. As shown in FIG. 19, an hour-glass jointshape results, which is commonly recognized as the most reliable shapefor increased resistance to thermally induced joint failures.

[0078] Due to the fact that columns 57 can be manufactured with anysolder, including eutectic tin-lead solder, the most of the volume ofthe contact 57 melts during the reflow, and the solder redistributesitself according to the surface area of its reinforcing wire skeletonand the surface area of its mating terminals. This feature allows one toachieve in some cases a self-alignment effect, e.g. the component ispulled into registration with the terminal array on a substrate due tosurface forces of solder wetting. This feature is in contrast to othertechniques for solder column utilization, which typically use highermelting temperature solder, and only the portions of solder depositedonto terminals on a substrate melt, which reduces the absolute value ofsolder-surface wetting forces.

[0079] The contacts of the present invention can be put on both sides ofan electronic package or a substrate for multiple interconnection tovarious devices. Alternatively, the contacts can be put on one side ofan electronic package for interconnection to a semiconductor device, andon the other side of the semiconductor package for subsequentinterconnection to a circuit board or any other substrate. FIG. 20depicts an electronic package 110, which has miniature solder columns570 for interconnecting a flip-chip semiconductor device, on top of thepackage, and solder columns 57 at the bottom, for subsequentinterconnection to a printed circuit board.

[0080] Spring contacts produced by the present invention are used as astandard means of interconnect between substrates and components whichhave matching patterns of terminals. In many cases it is desirable notto manufacture the contacts on either substrates or components, ordevices, as the process yield associated with contact manufacturingwould cause loss of costly devices, substrates or components. Oneembodiment of the present invention, illustrated in FIG. 21, providesfor a substantially planar interposer 120 with matching set of terminals97 on both sides thereof, and means 930 for connecting electrically thematching terminals on both of the sides. Protuberant resilient contacts59 are placed on contact carrying terminals 97 on both sides of theinterposer 120. This contact carrying structure is ready for demountableinterconnection of a variety of electronic components.

[0081] It will be apparent to those skilled in the art that widedeviations may be made from the foregoing preferred embodiments of theinvention without departing from a main theme of invention set forth inclaims which follow herein.

I claim:
 1. A method for mounting a protuberant conductive contact to anelectronic component, the method comprising sequential steps of:providing a wire having a continuous feed end, intimately bonding thefeed end to the component, forming from the bonded feed end a stem whichprotrudes from the component and has a first stem end thereat, severingthe stem at a second stem end to define a skeleton, depositing aconductive material to envelope the skeleton and adjacent surface of thecomponent.
 2. The method as claimed in claim 1, and immediately beforethe severing step intimately bonding the second stem end to thecomponent.
 3. A method for mounting a protuberant conductive contact toan electronic component, the method comprising sequential steps of:providing a wire having a continuous feed end, intimately bonding thefeed end to the component, forming from the bonded feed end a stem whichprotrudes from the component and has a first stem end thereat, severingthe stem at a second stem end to define a skeleton, depositing aconductive material to jacket the skeleton and adjacent surface of thecomponent.
 4. The method as claimed in claim 1, and immediately afterthe severing step, continuing sequentially the bonding step and theforming step and the severing step for a predetermined number of stemsto comprise the skeleton.
 5. The method as claimed in claim 4, andimmediately before each of the severing steps each of the second stemends is intimately bonded to the component.
 6. A method for mounting aprotuberant conductive contact to a conductive terminal on an electroniccomponent, the method comprising sequential steps of: providing a wirehaving a continuous feed end, intimately bonding the feed end to theterminal, forming from the feed end a stem which protrudes from theterminal and has a first stem end thereat, severing the stem at a secondstem end to define a skeleton, depositing a conductive material toenvelop the skeleton and adjacent surface of the terminal.
 7. The methodas claimed in claim 6, and immediately before the severing stepintimately bonding the second stem end to the terminal.
 8. The method asclaimed in claim 6, and immediately after the severing step, continuingsequentially the bonding step and the forming step and the severing stepfor a predetermined number of stems to comprise the skeleton.
 9. Themethod as claimed in claim 8, and immediately before each of thesevering steps each of the second stem ends is intimately bonded to theterminal.
 10. A method for mounting a protuberant conductive contact toa conductive terminal on an electronic component, the method comprisingsequential steps of: providing a wire having a continuous feed end,intimately bonding the feed end to the terminal, forming from the bondedfeed end a stem which protrudes from the terminal and has a first stemend thereat, severing the stem at a second stem end to define askeleton, depositing a conductive material to jacket the skeleton andadjacent surface of the terminal.
 11. The method as claimed in claim 10,and immediately before the severing step intimately bonding the secondstem end to the terminal.
 12. The method as claimed in claim 10, andimmediately after the last mentioned severing step continuingsequentially the bonding step and the forming step and the severing stepfor a predetermined number of stems to comprise the skeleton.
 13. Themethod as claimed in claim 12, and immediately before each of thesevering steps each of the second ends is intimately bonded to theterminal.
 14. A method for mounting a protuberant conductive contact toa conductive terminal on an electronic component, the method comprisingsequential steps of: providing a wire having a continuous feed end,intimately bonding the feed end to the terminal, forming from the bondedfeed end a stem which protrudes from the terminal and has a first stemend thereat, intimately bonding a second stem end to the terminal,sequentially continuing the forming step and the bonding step for apredetermined number of times, after the last bonding step severing thestem to define a skeleton, depositing a conductive material to envelopthe skeleton and adjacent surface of the terminal.
 15. A method formounting a protuberant conductive contact to a conductive terminal on anelectronic component, the method comprising sequential steps of:providing a wire having a continuous feed end, intimately bonding thefeed end to the terminal, forming from the bonded feed end a stem whichprotrudes from the terminal and has a first stem end thereat, bonding asecond stem end to a sacrificial member mounted in spaced relationshipfrom the component, severing the stem at the second stem end to define askeleton, depositing a conductive material to envelop the skeleton andat least adjacent surface of the component, eliminating the sacrificialmember.
 16. The method as claimed in claim 15, wherein during theeliminating step the second stem ends are severed from the sacrificialmember.
 17. The method as claimed in claim 6, 7, 8, 9, 14 or 15,performed on a plurality of the terminals on the electronic component.18. The method as claimed in claim 17, performed on a plurality of wireson a plurality of the terminals on the electronic component.
 19. Themethod as claimed in claim 17, with the bonding performed by applying atleast one of a group consisting of superambient pressure, superambienttemperature and ultrasonic energy.
 20. The method as claimed in claim17, wherein the severing is performed by melting the wire.
 21. Themethod as claimed in claim 17, wherein the forming steps and thesevering steps are performed by a wirebonding apparatus, and after thesevering steps but before the depositing step shaping the skeleton bymeans of a tool external to the apparatus.
 22. The method as claimed inclaim 17, wherein the severing of the second ends is performed bymechanical shearing.
 23. The method as claimed in claim 17, whereinduring the forming step the shape of the stems is determined by means ofa software algorithm in a control system of an automated wirebondingapparatus.
 24. The method as claimed in claim 6, 7, 8, 9 or 15,performed on a plurality of the terminals, wherein shape of the skeletonand mechanical properties of the conductive material are organizedcollectively to impart resilience to the protuberant conductive contact.25. The method as claimed in claim 24, wherein the conductive materialis provided with a multitude of microprotrusions on its surface.
 26. Themethod as claimed in claim 17, with the depositing step includingplacement of a plurality of layers each differing from one another. 27.The method as claimed in claim 24, wherein the depositing step includesplacement of a plurality of layers each differing from one another. 28.The method as claimed in claim 27, wherein at least one of the layerscomprising conductive material has a jagged topography in order toreduce contact resistance of the protuberant conductive contact whenmated to a matching terminal.
 29. The method as claimed in claim 17 or24, wherein the deposition is performed by means of electrochemicalplating in an ionic solution.
 30. The method as claimed in claim 6 or 8,performed on a plurality of the terminals and, wherein: the formingsteps result in a plurality of free-standing protuberant stems, thesevering steps are performed on the respective stems all in a commonplane.
 31. The method as claimed in claim 6 or 8, performed on aplurality of the terminals on at least one electronic component and,wherein: the terminals are in different planes, the forming steps resultin a plurality of free-standing protuberant stems, the severing stepsare performed on the respective stems all in a common plane.
 32. Themethod as claimed in claim 6 or 8, performed on a plurality of theterminals on at least one electronic component, wherein shapes of theskeleton and mechanical properties of the conductive material areorganized collectively to impart resilience to the protuberantconductive contacts, and the severing steps are performed on the stemsall in a common plane.
 33. The method as claimed in claim 17 or 24,wherein the cross-sectional area of the wire is rectangular.
 34. Themethod as claimed in claim 26 or 27, wherein the wire is made of a metalselected from a group consisting of gold, silver, beryllium, copper,aluminum, rhodium, ruthenium, palladium, platinum, cadmium, tin, lead,indium, antimony, phosphorous, boron, nickel, magnesium and alloysthereof, and wherein at least one of the layers of the conductivematerial is a metal selected from a group consisting of nickel,phosphorous, boron, cobalt, iron, chromium, copper, zinc, tungsten, tin,lead, bismuth, indium, cadmium, antimony, gold, silver, rhodium,palladium, platinum, ruthenium and alloys thereof.
 35. The method asclaimed in claim 6, 7, 8, or 14, performed on at least one terminal onan electronic component, wherein the wire is made primarily of a metalselected from a group consisting of gold, copper, aluminum, silver,lead, tin, indium and alloys thereof; the skeleton is coated with afirst layer of the conductive material selected from a group consistingof nickel, cobalt, boron, phosphorous, copper, tungsten, titanium,chromium, and alloys thereof; a top layer of the conductive material issolder selected from a group consisting of lead, tin, indium, bismuth,antimony, gold, silver, cadmium and alloys thereof.
 36. The method asclaimed in claim 26 or 27, wherein a layer reactive with material of thewire is interposed between the skeleton and the conductive material. 37.The method as claimed in claim 26 or 27, wherein the wire is gold andthe reactive layer is tin.
 38. An electronic component a first and asecond surface in which on at least one of the surfaces is provided aplurality of the terminals having protuberant conductive contactsmounted thereto and made by means of the method as claimed in any ofclaims 6, 7, 8, 14, 15 or 34.